1. Field of the Invention
The present invention relates to a method for rapidly cooling low melting, subliming granules obtained in a prilling process, by immersing these granules in a liquid which is inert and in which the granules are not soluble for a controlled amount of time. The partially solidified granules are then removed from the liquid before becoming fully cooled such that their remaining heat content causes any residual liquid on the granules to evaporate.
2. Description of Prior Art
Prilling is a well known process which is extensively used in the fertilizer industry for obtaining spherically shaped granules. It can be used if it is possible to melt the material, which, in the molten condition, is discharged through nozzles or perforated plates into an enclosed space known as a prilling tower. If the temperature difference between the atmospheric air and the melt is sufficiently high, the droplets can be cooled and solidified solely with the use of a countercurrent air stream. The solid granules are generally received in a container or in a liquid in which the material is not soluble.
If the temperature of the melt is relatively low, or if the height of the prilling tower is limited, the cooling can be accelerated by using a spray nozzle located in the inside of the enclosed space, which atomizes a coolant having a boiling point lower than the melting temperature of the substance. The liquid is sprayed onto the molten droplets, which are cooled by means of the latent heat of vaporization of the liquid. This process is described in U.S. Pat. No. 4,552,566.